Using google (or other search engines) for marketing purpose

We are developing a software product that can be tagged as "Project management tool", "Groupware", "Workflow tool", "Project Process software", etc...

If we map these descriptions to keywords, I would like to know which of them:

- Generate more interest in the potential market.
If possible, I would meassure this as the number of times that sombody looks up these keywords in google.
Does anybody have any idea of how to obtain such a figure?

- Provides more possibilities for obtaining a good position in the search engines
I would like to have a figure that somehow measures this. Any idea?

If I had these two figures I could balance them and choose the keywords that are more attractive to tag my product.

What do you think about this? Does it make sense?
How would you calculate this two figures?
How would you obtain them?